<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    let num1 = +prompt('请输入第一个数字：')
    let num2 = +prompt('请输入第二个数字：')
    let sp = prompt('请从 + - * / 其中选一个')
    switch (sp) {
      case '+':
        alert(num1 + num2)
        break
      case '-':
        alert(num1 - num2)
        break
      case '*':
        alert(num1 * num2)
        break
      case '/':
        alert(num1 / num2)
        break
      default:
        alert('不是哥们,别乱选')
    }
  </script>
</body>

</html>